In the food industry, a hydroxypropyl starch is widely used as a main raw material or auxiliary material of various processed food products. The hydroxypropyl starch is a modified starch obtained by acting propylene oxide on starch. Introduction of a hydroxypropyl group increases hydrophilicity, lowers temperature to initiate gelatinization, and improves performance in water retention, retrogradation stability, or freeze resistance. Therefore, taking advantage of these properties, it has been widely used in foods in general including instant foods such as LL (Long Life) noodles, various chilled and/or frozen foods, and bread.
On the other hand, a hydroxypropyl starch is known to exhibit resistance to an amylase and to be difficult to be digested. Non-patent Document 1 describes digestibility of the hydroxypropyl starch against a pancreatic amylase. It reports that a hydroxypropyl starch derived from corn starch, waxy corn starch, and high amylose corn starch showed, as its molar degree of substitution increases, a decrease in its digestive efficiency to the pancreatic amylase after gelatinization in all samples tested.
As an example using these properties, Patent Document 1 discloses that a method for producing a sugar substitute with low calorie and non-cariosity, which substitute is obtained by hydrolyzing the hydroxypropyl starch to a DE value of 1 to 30. Furthermore, Patent Document 2 discloses a hydrolysate of the hydroxypropyl starch having the DE value of 20 to 45 and containing at least 15% by mass of DP 2 to 6 and the use thereof as a low calorie bulking agent of a sweetener with high sweetness.
Thus, although there are prior arts on the hydrolysate of the hydroxypropyl starch, all are related to hydrolyzation products (mixtures) obtained by simply hydrolyzing the hydroxypropyl starch with an enzyme or acid. These contain many digestible components and cannot necessarily be sufficient as a low calorie dietary fiber material.
[Non-patent Document 1] Mohd et al., Starch/Staerke, 36 (7) 273-275 1984
[Patent Document 1] U.S. Pat. No. 3,505,110
[Patent Document 2] Japanese Patent Publication H07-14331 B